I suspect Cannon has done a lot of enhancements to the low light shooting in the current G series. Much faster lens and much higher usable ISO should get you better night shots. Go on DP Review
and search around, there are a bunch of cameras that are smaller and do very well against the 5D, the mirrorless offerings are much more compact and do an excellent job, but there is a reason the 5D is held in such high esteem, it's good. That being said I have seen photos shot with a number of cameras that are as good.